1. Field of the Invention
The present invention relates to a method for dynamically compensating for tool abrasion in a numerically-controlled (NC) machine tool.
2. Description of the Related Art
In an numerically-controlled (NC) machine tool, a machining process is performed by shifting (offsetting) a tool position by a tool dimension, such as a tool length, by a machining program. This is performed by describing a tool position offset amount (a tool length compensation amount) or a tool diameter compensation amount for performing a tool length compensation by a machining program of a G code. Because abrasion during a machining process changes tool dimension, such as a tool length, it is necessary to change a tool length compensation amount and the like relative to the tool abrasion.
Until recently, an operator has periodically measured a tool dimension and changed the tool length compensation amount and the like based on the measurement, or, as disclosed in Japanese laid-open publication Tokkaihei No.6-179151, a system automatically measures tool length at a specified time interval or a specified machining distance and then automatically updates a tool length compensation amount based on tool length measurement value obtained by the automatic measurement.
Tool abrasion gradually increases according to its operation time. According to the prior art, tool position compensation in relation to tool length and the like is performed at a certain time interval and tool position compensation amount does not change until the next tool position compensation. Because the tool position compensation is performed in stages of the time interval of tool position compensation, this method lacks in real-time performance.
A tool length measuring and compensating apparatus, disclosed in Japanese laid-open publication Tokkaihei No.6-179151, improves machining accuracy by shortening the time interval at which the tool compensation is performed by automatic measurement of the tool length. However, the shorter the interval of automatic measurement of the tool length is, the longer the time when the machining process is interrupted, thus decreasing machining efficiency.